1. Field of the Invention
The present invention generally relates to vertical transistors and method of manufacturing thereof, and more particularly, to a vertical transistor wherein source/drain regions are formed by using a self-alignment method without using a latest photolithography, channels are formed via a selective epitaxial growth (hereinafter, referred to as xe2x80x98SEGxe2x80x99) method and gate oxide films are formed at the both ends of channels to be more efficient than devices having the same channel length, and a method of manufacturing thereof.
2. Description of the Background Art
Although vertical devices have been proposed to overcome the limit in area of planar semiconductor devices, most of the proposed methods for manufacturing the devices are not suitable for mass production due to their complicated manufacturing process. Moreover, the methods require a photolithography and equipment thereof for forming the minimum line width. A method of forming a gate oxide film on sidewalls of a trench formed by etching a semiconductor substrate is used for vertical devices. However, in this method, the ratio of defect is high due to damage of silicon generated during the etching process, and it is difficult to perform ion-implantation process for implanting impurities because the source/drain regions are formed on the same plane as gate oxide films.
Accordingly, it is an object of the present invention to provide a vertical transistor wherein source/drain regions are formed using a self-alignment method without employing the latest photolithography, and channel regions are formed using a SEG method, and a method of manufacturing thereof, to reduce the damage and improve high integration.
In order to achieve the above-described object, there is provided a vertical transistor comprising: a source region formed on a semiconductor substrate; a drain region formed substantially above the source region; a vertical channel, one end of the channel being contact to the source region and the other end being contact to the drain region; and a gate electrode, formed on the substrate, surrounding the sides of the channel and the drain region, said gate electrode electrically isolated with the source region by a nitride pattern disposed therebetween, isolated with the drain region by a nitride spacer formed on the sidewalls of the drain region and isolated with channel by a gate oxide film covering the sidewalls of the channel and the exposed under surface of the drain region.
There is also provided a method of manufacturing a vertical transistor, comprising the steps of: (a) sequentially forming a nitride film and an oxide film on a semiconductor substrate; (b) forming an oxide film pattern by removing a predetermined portion of the oxide film to expose a portion of the nitride film; (c) forming a source region by implanting ions into the semiconductor substrate using the oxide film pattern as mask; (d) forming an oxide film spacer on the sidewalls of the oxide film pattern and selectively etching the nitride film using the oxide film spacer pattern as a mask to form a nitride film pattern exposing the substrate; (e) growing impurity-containing silicon on the exposed substrate so as to extrude over the oxide film pattern to form a first silicon layer which functions as a channel; (f) selectively growing impurity-free silicon layer on the first silicon layer to form a mushroom-shaped second silicon layer; (g) forming a drain region by implanting ions into the second silicon layer; (h) forming a nitride spacer on the sidewalls of the drain region; (i) removing the oxide film pattern and the oxide film spacer; (j) forming a gate insulating film covering the sidewalls of the first silicon layer and the exposed under surface of the drain region; (k) forming a polysilicon layer on the entire surface of the resultant structure; and (l) planarizing the polysilicon layer to expose the top portion of the drain region.